The present invention relates to a position detection device for detecting the position of a body which continuously moves, and more particularly to a device which is suitable for detecting the position of a movable body such as a sunroof or a package tray, a roof panel, back panel, luggage panel or the like which is mounted on a convertible vehicle.
It is a known technique to detect that one movable object has reached a given position using a combination of first and second micro-switches. Examples of such a technique are disclosed in Japanese Patent Publication No. 32489/1991 and Japanese Patent Publication No. 58029/1994.
These examples disclose a technique in which, in performing the closing operation of a sunroof panel, the sunroof panel is once stopped at a position just before a fully closed position so that the catching of a human body can be prevented. By changing over either the first switch or the second switch from an ON state to an OFF state or from the OFF state to the ON state, a judgement circuit detects that the sunroof panel has reached the position just before or right in front of fully closed position in response to signals from the first and second switches.
In the above-mentioned conventional examples, when either one of the first switch or the second switch breaks down, even when the sunroof panel has reached the position right in front of the fully closed position, there is a possibility that the signals from the first or second switch at this point of time become identical with signals obtained at other positions. In this case, it becomes difficult even to recognize that the sunroof panel has reached the position right in front of the fully closed position which is to be detected.
Of course, it may be possible to further add auxiliary switches to the first and second switches. In this case, when one of the first and second switches breaks down, the auxiliary switch may substitute for the broken first or second switch with a signal fed from the auxiliary switch. However, such a provision not only increases switches but also makes the judgement circuit complicated and hence, the provision is disadvantageous in terms of cost.
Accordingly, it is an object of the present invention to provide a position detection device which can overcome the above-mentioned drawbacks of the conventional examples.
According to the position detection device of the present invention, substantially, two switches, that is, first and second switches are simultaneously changed over and when only one of them is changed over, it is judged that a trouble has occurred. To be more specific, the position detection device of the present invention is provided with first and second switches which perform ON-OFF operations or output ON-OFF signals when an object which continuously moves reaches a given position. The position detection device detects the given position of the object in response to signals from the first and second switches when the first and second switches perform the ON-OFF operations.
Preferably, the position detection device of the present invention is further provided with switch changeover means which acts on the object such that the second switch performs the ON-OFF operation when the first switch performs the ON-OFF operation. To be more specific, the switch changeover means prevents the moving object from stopping in ON-OFF operation range (changeover range) of the first switch and the second switch or moves the object 1 when the object stops in the changeover range of the first switch and the second switch.